The ICU Collators (unlike the JDK ones) aren't thread safe: http://userguide.icu-project.org/collation/architecture , a little non-obvious since its not mentioned
in the javadocs, and its not clear if the docs apply to only the C code, but i looked
at the source and there is all kinds of internal state.
So in my opinion, we should clone the icu collators (which are passed in from the outside)
when creating a new TokenStream/AttributeImpl to prevent problems. This shouldn't be a big
deal since everything uses reusableTokenStream anyway.